Loans Held for Investment - Purchased Credit Impaired Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Loans Held for Investment
Unpaid Principal Balance	$ 12,154	$ 6,896
Business loans | Commercial and industrial
Loans Held for Investment
Unpaid Principal Balance	1,520	1,585
Business loans | Commercial owner occupied
Loans Held for Investment
Unpaid Principal Balance	3,598	98
Business loans | SBA
Loans Held for Investment
Unpaid Principal Balance	4,575	4,329
Real estate loans | Commercial non-owner occupied
Loans Held for Investment
Unpaid Principal Balance	0
Real estate loans | One-to-four family
Loans Held for Investment
Unpaid Principal Balance	1,178	849
Consumer Loans | Consumer loans
Loans Held for Investment
Unpaid Principal Balance	17
Acquired Banks
Loans Held for Investment
Unpaid Principal Balance	6,119	8,889
Acquired Banks | Business loans | Commercial and industrial
Loans Held for Investment
Unpaid Principal Balance	3,134	3,310
Acquired Banks | Business loans | Commercial owner occupied
Loans Held for Investment
Unpaid Principal Balance	1,016	1,262
Acquired Banks | Business loans | SBA
Loans Held for Investment
Unpaid Principal Balance	69	1,802
Acquired Banks | Real estate loans | Commercial non-owner occupied
Loans Held for Investment
Unpaid Principal Balance	1,122	1,650
Acquired Banks | Real estate loans | One-to-four family
Loans Held for Investment
Unpaid Principal Balance	0	255
Acquired Banks | Real estate loans | Construction/Land
Loans Held for Investment
Unpaid Principal Balance	768	600
Acquired Banks | Consumer Loans | Consumer loans
Loans Held for Investment
Unpaid Principal Balance	$ 10	$ 10